The experiments proposed in this application are designed to elucidate the mechanisms by which transforming growth factor beta1 (TGFbeta1) stimulates colony formation in soft agar. TGFbeta is unique in that regard since it is the only supplement when added to serum containing medium which consistently initiates and maintains soft agar colony growth. Since the ability of normal anchorage-dependent cultures to grow in an anchorage-independent manner is one of the best in correlates with tumorigenicity, the identification of specific regulatory genes might provide insights to the initial, and presumably rate limiting, events controlling neoplastic growth. It is our contention that expression of a unique program of genes, relative to that required for monolayer growth, is initiated by TGFbeta1 for soft agar growth; transformation might result from the constitutive or altered expression of these genes. Once these genes have been activated, the normal cellular machinery needed for cell division is operative. Moreover, inhibiting the expression of these genes may reestablish many aspects of normal growth control. We will test these hypotheses by 1) identifying unique cDNAs whose expression is specifically modulated during TGFbeta1-stimulated suspension growth; 2) determining whether a common set of genes are similarly expressed and required in various transformed cell lines; and 3) characterizing the cell cycle and growth factor regulated expression of specific proteins encoded by the clones isolated in the previous aims. These studies will not only increase our understanding of the events leading to tumorigenicity, but hopefully suggest new targets for therapeutic intervention.